Distance measurement device base on phase difference and distance measurement method thereof

ABSTRACT

A distance measurement device including a pixel array and a cover layer is provided. The cover layer is covered on the pixel array. The cover layer includes a first cover pattern covering on a first area of a plurality of first pixels and a second cover pattern covering on a second area of a plurality of second pixels. The first area and the second area are rectangles of mirror symmetry along a first direction.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan PatentApplication Serial Number 104121577, filed on Jul. 2, 2015, the fulldisclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Disclosure

This disclosure generally relates to an optical sensing element, moreparticularly, to a distance measurement device based on phase differenceand a distance measurement method thereof.

2. Description of the Related Art

In general, a distance measurement system employs a light source andcalculates an object distance according to energy of light beam of thelight source reflected back by the object. Traditionally, it is able tocalculate the distance using the triangulation method or time-of-flight(TOF) technique. However, the above methods require a higher cost andlarger system size.

In addition, the development of gesture recognition generally removesthe background image at first by using a 3D image in order to separatethe foreground image. In this technique, two image sensors are used suchthat the size and cost of a gesture recognition module can not beeffectively reduced.

As mentioned above, the present disclosure obtains a 3D image by usingthe phase detection, and an additional illumination light (as used inthe TOF technique mentioned above) is not required. Meanwhile, in theproposed technique of the present disclosure, the distance measurementand the gesture recognition are implemented by only employing a singleimage sensor.

SUMMARY

Accordingly, the present disclosure provides an optical distancemeasurement device and a distance measurement method thereof withadvantages of low cost and small size.

The present disclosure provides a distance measurement device includinga condensing lens, an image sensor and a processor. The condensing lenshas a predetermined focal length. The image sensor is configured todetect light passing through the condensing lens and output an imageframe. The image sensor includes a pixel matrix, a cover layer and aplurality of microlenses. The pixel matrix includes a first pixel groupand a second pixel group arranged in a first direction and a seconddirection. The cover layer covers upon a first region of a plurality offirst pixels of the first pixel group and upon a second region of aplurality of second pixels of the second pixel group, wherein the firstregion and the second region are rectangles of mirror symmetry along thefirst direction. Each of the microlenses is aligned with at least one ofone of the first pixels and one of the second pixels. The processor isconfigured to calculate a depth of an image region in the image frame.

The present disclosure further provides a distance measurement method ofa distance measurement device. The distance measurement device includesa first pixel group, a second pixel group and a plurality ofmicrolenses. The first pixel group and the second pixel group receiveincident light of different phases respectively through a first part anda second part of the microlenses. The distance measurement methodincludes the steps of: outputting, by the first pixel group and thesecond pixel group, an image frame according to a predetermined focallength; dividing the image frame into a first subframe and a secondsubframe, wherein the first subframe is associated with the first pixelgroup and the second subframe is associated with the second pixel group;calculating a first offset of a corresponded image region in the firstsubframe and the second subframe; and calculating a first depth of theimage region according to the first offset.

The present disclosure further provides a distance measurement deviceincluding a pixel matrix and a cover layer. The pixel matrix includes afirst pixel group, a second pixel group, a third pixel group and afourth pixel group arranged along a first direction and a seconddirection. The cover layer covers upon the pixel matrix and includes afirst cover pattern covering upon a first region of a plurality of firstpixels of the first pixel group, a second cover pattern covering upon asecond region of a plurality of second pixels of the second pixel group,a third cover pattern covering upon a third region of a plurality ofthird pixels of the third pixel group, and a fourth cover patterncovering upon a fourth region of a plurality of fourth pixels of thefourth pixel group, wherein the first region and the second region arerectangles of mirror symmetry along the first direction, and the thirdregion and the fourth region are rectangles of mirror symmetry along thesecond direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the present disclosurewill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

FIG. 1 is a schematic block diagram of a distance measurement deviceaccording to one embodiment of the present disclosure.

FIGS. 2A-2B are cross sectional views of an image sensor and acondensing lens of a distance measurement device according to someembodiments of the present disclosure.

FIG. 3 is a schematic diagram of a pixel matrix and a cover layer of adistance measurement device according to one embodiment of the presentdisclosure.

FIG. 4 is an operational schematic diagram of a distance measurementmethod according to one embodiment of the present disclosure.

FIGS. 5A-5D are schematic diagrams of a pixel matrix and a cover layerof a distance measurement device according to some embodiments of thepresent disclosure.

FIG. 6 is a flow chart of a distance measurement method according to anembodiment of the present disclosure.

FIG. 7 is a flow chart of a distance measurement method according toanother embodiment of the present disclosure.

FIG. 8 is an operational schematic diagram of a distance measurementmethod according to an alternative embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

It should be noted that, wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Referring to FIGS. 1 and 2A-2B, FIG. 1 is a schematic block diagram of adistance measurement device 1 according to one embodiment of the presentdisclosure; and FIGS. 2A-2B are cross sectional views of an image sensorand a condensing lens of a distance measurement device according to someembodiments of the present disclosure. The distance measurement device 1includes a condensing lens 10, an image sensor 11 and a processor 13. Insome embodiments, the processor 13 is, for example, disposed in a chiptogether with the image sensor 11. In some embodiments, the processor 13is an external processing unit of the image sensor 11, and configured toreceive and process an image frame F captured by the image sensor 11 forcalculating a depth of at least one image region or constructing a depthmap of the image frame F, i.e., a depth map of a plurality of imageregions. For example, the processor 13 is a microprocessor (MCU), acentral processing unit (CPU), a digital signal processor (DSP) or thelike for processing the image frame F outputted by the image sensor 11.

The condensing lens 10 is arranged, for example, inside a lens of animage capturing device (e.g., a camera). The condensing lens 10 is asingle lens or a lens set arranged along an optical axis withoutparticular limitations. For simplification purposes, a single lens isshown herein. The condensing lens 10 is used as a lens window configuredto collect light L from an object 9 and guide the light L to the imagesensor 11. A distance between the condensing lens 10 and the imagesensor 11 is preferably equal to a first focal length of the condensinglens 10 (e.g., the focal length at a side of the image sensor 11).

The image sensor 11 detects light passing through the condensing lens 10based on a predetermined focal length and outputs an image frame F. Theimage sensor 11 includes a pixel matrix 111 (e.g., an 8×8 pixel matrixis shown herein for illustration purposes), a cover layer 113 and aplurality of microlenses 115, wherein the cover layer 113 is patternedto cover upon at least a part of a plurality of pixels included in thepixel matrix 111 such that uncovered regions of the pixels receiveincident light of different phases through different parts of themicrolenses 115. The predetermined focal length herein is referred to afocal length formed by both the condensing lens 10 and the microlenses115, and at a light incident side of the condensing lens 10. Thepredetermined focal length is sometimes referred to a predeterminedfocal length of the condensing lens 10 or of the image sensor 11 forabbreviation.

The inventor noticed that when an object 9 reflects the light L at asecond focal length of the condensing lens 10 (e.g., a focal length atthe other side of the image sensor 11, i.e. the predetermined focallength) to the distance measurement device 1, an object image in theimage frame F outputted from the image sensor 11 does not have aposition shift; whereas, when the object 9 is not at the second focallength of the condensing lens 10, the object image in the image frame Foutputted by the image sensor 11 has a position shift toward differentdirections in subframes corresponding to pixels of different coverpatterns, illustrated hereinafter with an example. Accordingly, a depthdifference of the object 9 deviated from the predetermined focal lengthis identifiable according to the position shift so as to obtain adistance (i.e. a depth) from the image sensor 11 (or the condensing lens10) to implement a distance measurement device 1 of the presentdisclosure.

Referring to FIG. 3, it is a schematic diagram of a pixel matrix and acover layer of a distance measurement device according to one embodimentof the present disclosure. In one embodiment, the pixel matrix 111includes a first pixel group P₁ and a second pixel group P₂ arranged ina first direction (e.g., X direction) and a second direction (e.g., Ydirection). It should be mentioned that in the present disclosure, thefirst pixel group P₁ and the second pixel group P₂ have differentcovered regions. For example, in a monochromatic image sensor, pixelstructures of the first pixel group P₁ and the second pixel group P₂ areidentical, whereas the cover patterns thereupon are different. Forexample, in a color image sensor, both the first pixel group P₁ and thesecond pixel group P₂ include, for example, red pixels (e.g., forming ared filter on a pixel), green pixels (e.g., forming a green filter on apixel), blue pixels (e.g., forming a blue filter on a pixel) or pixelsof other colors, but the cover patterns upon the first pixel group P₁and the second pixel group P₂ are different.

The cover layer 113 is formed, for example, by the metal layer which isused as electrical paths (e.g., at least one layer of M1 to M10 of theCMOS manufacturing process), an opaque layer different from the metallayer or a combination thereof without particular limitations. In thisembodiment, the cover layer 113 covers upon a first region A1 of aplurality of first pixels of the first pixel group P₁ and upon a secondregion A2 of a plurality of second pixels of the second pixel group P₂.In FIG. 3, the second region A2 is at a side along the first direction(e.g., X direction) and the first region A1 is at a side of an inversedirection of the first direction such that the first region A1 of thefirst pixel group P₁ and the second region A2 of the second pixel groupP₂ form rectangles of mirror symmetry along the first direction. Inaddition, the first pixel group P₁ has an uncovered region A1′ outsidethe first region A1, and the second pixel group P₂ has an uncoveredregion A2′ outside the second region A2, wherein the uncovered regionsA1′ and A2′ receive incident light of different phases respectivelythrough different parts of the microlenses 115.

For example in FIG. 3, the first region A1 is shown at a left side ofthe first pixels and the second region A2 is shown at a right side ofthe second pixels. It should be mentioned that although FIG. 3 showsthat the first region A1 and the second region A2 are 50% of an area ofa single pixel, it is only intended to illustrate but not to limit thepresent disclosure. In other embodiments, the first region A1 and thesecond region A2 are 5% to 95% of an area of a single pixel withoutparticular limitations.

The microlenses 115 are aligned with at least one of one of the firstpixels and one of the second pixels. In some embodiments, themicrolenses 115 are respectively aligned with each of the first pixelsand each of the second pixels, as shown in FIG. 2A. In anotherembodiment, each of the microlenses 115 is aligned with the uncoveredregion A1′ outside the first region A1 of the first pixels and theuncovered region A2′ outside the second region A2 of the second pixelsat the same time, as shown in FIG. 2B. Accordingly, the first pixelgroup P₁ and the second pixel group P₂ receive incident light ofdifferent phases respectively through a first part of the microlenses115 (e.g., the right part of the microlenses 115) and a second part ofthe microlenses 115 (e.g., the left part of the microlenses 115). Itshould be mentioned that although FIGS. 2A and 2B show that theuncovered regions (e.g., A1′ and A2′) of the first pixel group P₁ andthe second pixel group P₂ are substantially a half of the microlenses115, they are only intended to illustrate but not to limit the presentdisclosure. It is appreciated that the part of light capable ofpenetrating the microlenses 115 to reach the uncovered regions isdetermined according to the first region A1 and the second region A2 ofthe cover layer 113. In the present disclosure, the first part and thesecond part of the microlenses 115 are selected to be 5% to 95% of themicrolenses 115.

The processor 13 is used to calculate a depth of at least one imageregion in an image frame F, e.g., dividing the image frame F into afirst subframe and a second subframe, calculating an offsetcorresponding to the image region according to the first subframe andthe second subframe, and calculating the depth according to the offset,wherein the first subframe is associated with the first pixel group P₁and the second subframe is associated with the second pixel group P₂.More specifically, the first subframe is formed by gray level dataoutputted by the first pixel group P₁ and second subframe is formed bygray level data outputted by the second pixel group P₂.

Referring to FIGS. 1 to 4, FIG. 4 is an operational schematic diagram ofa distance measurement method according to one embodiment of the presentdisclosure. In one embodiment, the processor 13 includes a framedivision module 131, an offset calculation module 133, a depthcalculation module 135 and a storage unit 137, wherein the framedivision module 131, the offset calculation module 133 and the depthcalculation module 135 are implemented by software and/or hardwarewithout particular limitations. For illustration purposes, the framedivision module 131, the offset calculation module 133 and the depthcalculation module 135 are shown to be separated from each other, butoperations thereof are considered to be accomplished by the processor13. The storage unit 137 previously stores a relationship, e.g., formedas a lookup table, of a plurality of offsets with respect to a pluralityof depth differences distanced from the predetermined focal length forthe depth calculation module 135 to calculate the depth of at least oneimage region according to the calculated offset.

More specifically, the predetermined focal length is already known. Whenan offset corresponding to an image region is obtained, a depthdifference of the image region from the predetermined focal length isobtainable according to the lookup table, and the depth of the at leastone image region is obtainable by adding the depth difference to orsubtracting the depth difference from the predetermined focal length.

In FIG. 4, a dot object 9 located at a light incident side of thecondensing lens 10 is taken as an example for illustration. The imagesensor 11 captures, based on a predetermined focal length, and outputsan image frame F to the processor 13. The frame division module 131divides the image frame F into a first subframe F_(P1) and a secondsubframe F_(P2), wherein the first subframe F_(P1) is associated withthe first pixel group P₁ and the second subframe F_(P2) is associatedwith the second pixel group P₂. When the object 9 is located at thesecond focal length (i.e. the predetermined focal length) of thecondensing lens 10, image regions associated with the object 9 in thefirst subframe F_(P1) and the second subframe F_(P2) are substantiallyat corresponding positions with no offset. When the object 9 is notlocated at the second focal length of the condensing lens 10, the imageregions associated with the object 9 in the first subframe F_(P1) andthe second subframe F_(P2) have an offset therebetween and are not atcorresponding positions. For example, FIG. 4 shows that a first imageregion I₉₁ in the first subframe F_(P1) shifts rightward from a centerline (e.g., the dashed line) by S₁, and a second image region I₉₂ in thesecond subframe F_(P2) shifts leftward from a center line (e.g., dashedline) by S₂. The offset calculation module 133 calculates an offsetbetween S₁ and S₂, e.g., (S₁−S₂). It is appreciated that the offset isnot limited to be calculated based on the center line, and the centerline used herein is only taken as an example. It is also possible tocalculate the offset by using the block matching or motion detectionwithout particular limitations as long as the offset betweencorresponded image regions (e.g., I₉₁ and I₉₂) in the first subframeF_(P1) and the second subframe F_(P2) are obtainable.

It should be mentioned that although FIG. 4 shows that the first imageregion I₉₁ shifts rightward by S₁ and the second image region I₉₂ shiftsleftward by S₂, it is only intended to illustrate but not to limit thepresent disclosure. The shift direction of the image regioncorresponding to the object 9 is determined according to whether theobject 9 is close to or away from the condensing lens 10 from the secondfocal length as well as the covered regions (e.g., A1 and A2) of thefirst pixel group P₁ and the second pixel group P₂. For example, FIG. 4shows a condition under the arrangement of FIG. 2A when the object 9 isfar from the condensing lens 11 from the second focal length thereof.

The depth calculation module 135 calculates a depth of the image regionaccording to the offset between S₁ and S₂ in conjunction with arelationship of a plurality of offsets with respect to a plurality depthdifferences deviated from the predetermined focal length previouslystored in the storage unit 137. For example, when S₁ and S₂ aresubstantially identical to zero, it is able to identify that a depth ofthe image region is substantially equal to the second focal length,which is known previously. In one embodiment, said relationship is arelation of offsets between S₁ and S₂ with respect to depth differencesfrom the predetermined focal length. Meanwhile, under the arrangement ofFIG. 2A and assuming that a right side of a center line in FIG. 4. ispositive and a left side of the center line in FIG. 4 is negative, when(S₁−S₂) is a negative value, it means that the depth is smaller than thesecond focal length; whereas, when (S₁−S₂) is a positive value, it meansthat the depth is larger than the second focal length. If the offset isnot calculated by subtraction, a direction of the depth difference isdetermined according to a direction of shift.

It should be mentioned that in this embodiment the image region is shownas a circle (corresponding to the dot object 9) for illustrationpurposes, but the present disclosure is not limited thereto. The imageregion is any feature (e.g., edges) in the image frame F capable ofshowing an offset without particular limitations.

In addition, to increase the identification accuracy, the processor 13further calibrates brightness of the first subframe F_(P1) and thesecond subframe F_(P2) to be substantially identical by a shadingalgorithm. Accordingly, it is able to correctly identify correspondedimage regions (e.g., image regions having identical brightness) in thefirst subframe F_(P1) and the second subframe F_(P2), e.g., I₉₁ and I₉₂.For example, when the image frame F contains a plurality of pixelregions, depths of the plurality of pixel regions are calculatedrespectively by using the same method mentioned above so as to constructa depth map.

In addition, FIG. 3 shows that the first pixel group P₁ and the secondpixel group P₂ are arranged alternatively along the X direction. Inother embodiments, it is possible that the first pixel group P₁ and thesecond pixel group P₂ are arranged alternatively along the Y direction;in this case, the dashed lines in FIG. 4 are changed to horizontal linesand the image regions are shifted upward and downward from the centerline. Since only the shift direction is different but the calculationitself is not changed, details thereof are not repeated herein.

Referring to FIGS. 5A and 5B, they are schematic diagrams of a pixelmatrix and a cover layer of a distance measurement device according tosome embodiments of the present disclosure. In this embodiment, thepixel matrix 111 further includes a third pixel group P₃ and a fourthpixel group P₄ arranged in the first direction (e.g., X direction) andthe second direction (e.g., Y direction). The cover layer 113 furthercovers upon a third region A3 of a plurality of third pixels of thethird pixel group P₃ and upon a fourth region A4 of a plurality offourth pixels of the fourth pixel group P₄, wherein the third region A3is at a side along the second direction (e.g., Y direction) and thefourth region A4 is at a side along an inverse direction of the seconddirection. For example in FIGS. 5A to 5B, the third region A3 is at anupper side of the third pixels and the fourth region A4 is at a lowerside of the fourth pixels such that the third region A3 and the fourthregion A4 form rectangles of mirror symmetry along the second direction.

More specifically, in the embodiments of FIGS. 5A to 5B, the cover layer113 covers upon the pixel matrix 111 and includes a first cover patterncovering upon a first region A1 of a plurality of first pixels of thefirst pixel group P₁, a second cover pattern covering upon a secondregion A2 of a plurality of second pixels of the second pixel group P₂,a third cover pattern covering upon a third region A3 of a plurality ofthird pixels of the third pixel group P₃, and a fourth cover patterncovering upon a fourth region A4 of a plurality of fourth pixels of thefourth pixel group P₄, wherein the first region A1 and the second regionA2 form rectangles of mirror symmetry along a first direction andadjacent to each other along a diagonal direction of the pixel matrix,and the third region A3 and the fourth region A4 form rectangles ofmirror symmetry along a second direction and adjacent to each otheralong another diagonal direction of the pixel matrix. In one embodiment,the first direction is perpendicular to the second direction.

In this embodiment, one first pixel P₁ (P₁′), one second pixel P₂ (P₂′),one third pixel P₃ (P₃′) and one fourth pixel P₄ (P₄′) adjacent to eachother form a sub pixel group, and the first region A1 (A1′), the secondregion A2 (A2′), the third region A3 (A3′) and the fourth region A4(A4′) in the sub pixel group have substantially identical areas, whereinthe first pixels (i.e. the first cover pattern) are adjacent to thesecond pixels (i.e. the second cover pattern) along a diagonaldirection, and the third pixels (i.e. the third cover pattern) areadjacent to the fourth pixels (i.e. the fourth cover pattern) alonganother diagonal direction.

In one embodiment, all the first region A1, the second region A2, thethird region A3 and the fourth region A4 of the pixel matrix 111 havesubstantially identical areas (as shown in FIGS. 5A to 5B), e.g., 5% to95% of an area of a single pixel.

Referring to FIGS. 5C to 5D, they are schematic diagrams of a pixelmatrix and a cover layer of a distance measurement device according tosome embodiments of the present disclosure. In other embodiments, thecovered areas in two sub pixel groups adjacent along the first direction(e.g., X direction) and the second direction (e.g., Y direction) aredifferent. In some embodiments, the first region to the fourth region ofa first sub pixel group (e.g., formed by pixels P₁ to P₄) are 50% of anarea of a single pixel, and the first region to the fourth region of asecond sub pixel group (e.g., formed by pixels P₁″ to P₄″) are 5% to 45%of an area of a single pixel (as shown in FIG. 5D). In some embodiments,the first region to the fourth region of a first sub pixel group (e.g.,formed by pixels P₁ to P₄) are 50% of an area of a single pixel, and thefirst region to the fourth region of a second sub pixel group (e.g.,formed by pixels P₁′ to P₄′) are 55% to 95% of an area of a single pixel(as shown in FIG. 5C).

According to the embodiments of FIGS. 5A to 5D, in addition to theoffsets in two directions are obtainable according to the pixelsarranged along the X direction (e.g., first pixels P₁, P₁′ and P₁″ andsecond pixels P₂, P₂′ and P₂″) and pixels arranged along the Y direction(e.g., third pixels P₃, P₃′ and P₃″ and fourth pixels P₄, P₄′ and P₄″),the objects of confirming depths and having different depth resolutionsare implemented (described hereinafter with an example).

Referring to FIG. 6, it is a flow chart of a distance measurement methodof a distance measurement device according to one embodiment of thepresent disclosure. The distance measurement device of this embodimentincludes a first pixel group P₁, a second pixel group P₂, a third pixelgroup P₃, a fourth pixel group P₄ (as shown in FIGS. 5A to 5D) and aplurality of microlenses 115 (as shown in FIGS. 2A to 2B). The firstpixel group P₁ and the second pixel group P₂ receive incident light ofdifferent phases respectively through a first part and a second part ofthe microlenses 115, and the third pixel group P₃ and the fourth pixelgroup P₄ receive incident light of different phases respectively througha third part and a fourth part of the microlenses 115, wherein the firstpart and the second part are two opposite sides of the microlenses 115along a first axis (e.g., X direction), and the third part and thefourth part are two opposite sides of the microlenses 115 along a secondaxis (e.g., Y direction) as shown in FIG. 8.

The distance measurement method of this embodiment includes the stepsof: outputting an image frame based on a predetermined focal length by afirst pixel group, a second pixel group, a third pixel group and afourth pixel group (Step S61); dividing the image frame into a firstsubframe, a second subframe, a third subframe and a fourth subframe(Step S62); calculating a first offset according to the first subframeand the second subframe, and calculating a second offset according tothe third subframe and the fourth subframe (Step S63); and calculating afirst depth according to the first offset and calculating a second depthaccording to the second offset (Step S64).

Referring to FIGS. 1, 5A to 5D, 6 and 8, the implementation of thisembodiment is illustrated hereinafter.

Step S61: All pixels of the pixel matrix 111 detect light L passingthrough the condensing lens 10 with a predetermined focal length suchthat the first pixel group P₁, the second pixel group P₂, the thirdpixel group P₃ and the fourth pixel group P₄ output an image frame F.That is, the image frame F is formed by image data (e.g., gray values)outputted by the first pixel group P₁, the second pixel group P₂, thethird pixel group P₃ and the fourth pixel group P₄.

Step S62: The frame division module 131 of the processor 13 then dividesthe image frame F into a first subframe F₁, a second subframe F₂, athird subframe F₃ and a fourth subframe F₄, wherein the first subframeF₁ is associated with the first pixel group P₁ (i.e. formed by graylevel data outputted by the first pixel group P₁), the second subframeF₂ is associated with the second pixel group P₂ (i.e. formed by graylevel data outputted by the second pixel group P₂), the third subframeF₃ is associated with the third pixel group P₃ (i.e. formed by graylevel data outputted by the third pixel group P₃), and the fourthsubframe F₄ is associated with the fourth pixel group P₄ (i.e. formed bygray level data outputted by the fourth pixel group P₄).

Step S63: The offset calculation module 133 of the processor 13 thencalculates a first offset of corresponded image regions in the firstsubframe F₁ and the second subframe F₂ (e.g., an offset between S₁ andS₂) and a second offset of corresponded image regions in the thirdsubframe F₃ and the fourth subframe F₄ (e.g., an offset between S₃ andS₄). As mentioned above, the calculation of the first offset and thesecond offset is calculated using the subtraction, block matching,motion detection or the like.

Step S64: The depth calculation module 135 of the processor 13calculates a first depth D₁₂ according to the first offset andcalculates a second depth D₄₃ according to the second offset. In thisembodiment, the first depth D₁₂ is obtained, for example, according tothe offset in a first direction referring to a lookup table, and thesecond depth D₄₃ is obtained, for example, according to the offset in asecond direction referring to the lookup table, wherein the firstdirection is perpendicular to the second direction. As mentioned above,a lookup table previously stores a relationship of a plurality ofoffsets with respect to a plurality of depth differences distanced fromthe predetermined focal length.

Similarly, before calculating the first offset and the second offset,the processor 13 further calibrates brightness of the first subframe F₁and the second subframe F₂ to be substantially identical and calibratesbrightness of the third subframe F₃ and the fourth subframe F₄ to besubstantially identical using a shading algorithm to correctly identifythe corresponded object regions.

The above embodiment of FIG. 6 operates according to the arrangement ofFIGS. 5A and 5B, and thus only the left part of FIG. 8 is considered.The embodiment blow of FIG. 7 operates according to the arrangement ofFIG. 5C and thus the whole of FIG. 8 is considered. The operationaccording to the arrangement of FIG. 5D is similar to that according tothe arrangement of FIG. 5C and thus details thereof are not repeatedherein.

Referring to FIG. 7, it is a flow chart of a distance measurement methodof a distance measurement device according to another embodiment of thepresent disclosure. In this embodiment, one first pixel P₁ (P₁′), onesecond pixel P₂ (P₂′), one third pixel P₃ (P₃′) and one fourth pixel P₄(P₄′) adjacent to each other form a sub pixel group. In two sub pixelgroups adjacent along the first axis (e.g., X direction) and the secondaxis (e.g., Y direction), when the first region to the fourth region ina first sub pixel group (e.g., P₁ to P₄) are smaller than the firstregion to the fourth region in a second sub pixel group (e.g., P₁′ toP₄′), and when the first depth D₁₂ and the second depth D₄₃ are obtainedaccording to the first sub pixel group (e.g., P₁ to P₄), the distancemeasurement method of this embodiment includes the steps of: calculatinga first depth and a second depth according to the first sub pixel group(Step S641); calculating a third depth and a fourth depth according tothe second sub pixel group (Step S642); confirming the first depth withthe third depth (Step S643); and confirming the second depth with thefourth depth (Step S644), wherein the Step S641 is to perform the stepsof FIG. 6, and the Step S642 is similar to FIG. 6 only the calculatedsub pixel group is different. In addition, the Steps S641 and S642 arepossible to operate simultaneously as shown in FIG. 8. The Step S642 isfurther illustrated below, whereas the Step S641 is not repeated herein.

All pixels of the pixel matrix 111 detect light penetrating thecondensing lens 10 with a predetermined focal length, and the firstpixel group P₁′, the second pixel group P₂′, the third pixel group P₃′and the fourth pixel group P₄′ output a part of an image frame F. Theother part of the image frame F is outputted by the first pixel groupP₁, the second pixel group P₂, the third pixel group P₃ and the fourthpixel group P₄. That is, The image frame F is formed together by imagedata (e.g., gray values) outputted by the first pixel group P₁, thesecond pixel group P₂, the third pixel group P₃ and the fourth pixelgroup P₄ as well as the first pixel group P₁′, the second pixel groupP₂′, the third pixel group P₃′ and the fourth pixel group P₄′.

The frame division module 131 of the processor 13 further divides theimage frame F into a first subframe F₁′, a second subframe F₂′, a thirdsubframe F₃′ and a fourth subframe F₄′, wherein the first subframe F₁′is associated with the first pixel group P₁′ (i.e. formed by gray leveldata outputted by the first pixel group PC), the second subframe F₂′ isassociated with the second pixel group P₂′ (i.e. formed by gray leveldata outputted by the second pixel group P₂′), the third subframe F₃′ isassociated with the third pixel group P₃′ (i.e. formed by gray leveldata outputted by the third pixel group P₃′), and the fourth subframeF₄′ is associated with the fourth pixel group P₄′ (i.e. formed by graylevel data outputted by the fourth pixel group P₄′).

The offset calculation module 133 of the processor 13 then calculates afirst offset between corresponded image regions in the first subframeF₁′ and the second subframe F₂′ (e.g., an offset between S₁′ and S₂′),and calculates a second offset between corresponded image regions in thethird subframe F₃′ and the fourth subframe F₄′ (e.g., an offset betweenS₃′ and S₄′). The calculation has been illustrated above, and thusdetails thereof are not repeated herein.

The depth calculation module 135 of the processor 13 calculates a thirddepth D₁₂′ according to the first offset and calculates a fourth depthD₄₃′ according to the second offset as shown in FIG. 8. Similarly, thethird depth D₁₂′ is obtained according to the offset along a firstdirection by checking a lookup table and the fourth depth D₄₃′ isobtained according to the offset along a second direction by checkingthe lookup table.

In some cases, it is possible that one offset (e.g., the offset betweenS₁ and S₂ or between S₁′ and S₂′) corresponds to two depths, and thus inthis embodiment two sets of different sub pixel groups are used toconfirm one correct depth so as to improve the identification accuracy.For example in the Step S643, the third depth D₁₂′ is used to confirmthe first depth D₁₂, and in the Step S644, the fourth depth D₄₃′ is usedto confirm the second depth D₄₃, or vice versa.

In this embodiment, as the first sub pixel group and the second subpixel group have different covered areas, the first depth D₁₂ and thesecond depth D₄₃ have a first resolution, and the third depth D₁₂′ andthe fourth depth D₄₃′ have a second resolution different from the firstresolution so as to improve the applicable range.

It should be mentioned that although the distance measurement method ofFIG. 6 is illustrated by using the schematic diagram of FIG. 8, thepresent disclosure is not limited thereto. When the cover pattern of thecover layer 113 is like FIG. 3, the Steps S61 to S64 do not include thethird and fourth pixel groups or do not include the first and secondpixel groups, and operate only according to FIG. 4. Accordingly, theoperating method includes the steps of: outputting an image frame by afirst pixel group and a second pixel group with a predetermined focallength; dividing the image frame into a first subframe and a secondsubframe; calibrating the first subframe and the second subframe to havesubstantially identical brightness; calculating an offset of acorresponded image region respectively in the first subframe and thesecond subframe; and calculating a depth of the image region accordingto the offset. Or the operating method includes the steps of: outputtingan image frame by a third pixel group and a fourth pixel group with apredetermined focal length; dividing the image frame into a thirdsubframe and a fourth subframe; calibrating the third subframe and thefourth subframe to have substantially identical brightness; calculatingan offset of a corresponded image region respectively in the thirdsubframe and the fourth subframe; and calculating a depth of the imageregion according to the offset.

More specifically, it is possible that the present disclosure calculatesdepths of different image regions according to different arrangements ofthe cover layer 113. In addition, the processor 13 determines the depthof the image region to be calculated according to differentapplications, e.g., calculating the depth according to only two pixelgroups but ignoring pixel data of other pixel groups.

In the present disclosure, as the first pixel group includes a pluralityof first pixels, the first pixel group and the first pixels are bothindicated by a reference numeral P₁. Similarly, the second pixel groupand the second pixels are both indicated by a reference numeral P₂, thethird pixel group and the third pixels are both indicated by a referencenumeral P₃, and the fourth pixel group and the fourth pixels are bothindicated by a reference numeral P₄.

In addition, when the distance measurement device 1 is used to detectone object, corresponding to a two dimensional position of an objectimage in the image frame, the processor 13 further calculates a threedimensional coordinate of the object according to the two dimensionalposition and an object depth.

In addition, when the distance measurement device 1 is used to detect aplurality of objects, it is possible to further calculate both thedepths and three dimensional coordinates of the plurality of objectsaccording to the distance measurement methods of FIGS. 6 and 7.

In addition, although the present disclosure takes a dot object 9 as anexample for illustration, the present disclosure is not limited thereto.Actually, the distance measurement device 1 does not necessary torecognize any object but respectively calculates depths of every imageregion according to the above distance measurement methods to constructa depth map of the image frame F.

It should be mentioned that values in above embodiments, e.g., the sizeand area ratio of the image frame F, are only intended to illustrate butnot to limit the present disclosure. The element scale and arrangementas well as the direction in the drawings of the present disclosure areonly intended to illustrate but not to limit the present disclosure.

It should be mentioned that in the above embodiments although the coverlayer 113 is shown to be covered upon every pixel, it is only intendedto illustrate but not to limit the present disclosure. In otherembodiments, the cover layer 111 covers upon only a part of pixels ofthe pixel matrix 111, wherein outputted data of the part of pixels beingcovered by the cover layer 113 is used to identify a depth of the imageregion, and outputted data of the uncovered pixels is for otherfunctions, e.g., the gesture recognition.

As mentioned above, the conventional distance measurement system and thegesture recognition system need a higher cost and size, and generally anadditional light source is required. Therefore, the present disclosureprovides an optical distance measurement device (FIG. 1) and a distancemeasurement method thereof (FIGS. 6-7) that calculate the depth of imageregions according to the offset of image positions caused by the phasedifference between incident light penetrating different parts ofmicrolenses. As a light source is no longer required, it has theadvantages of low cost and small size.

Although the disclosure has been explained in relation to its preferredembodiment, it is not used to limit the disclosure. It is to beunderstood that many other possible modifications and variations can bemade by those skilled in the art without departing from the spirit andscope of the disclosure as hereinafter claimed.

What is claimed is:
 1. A distance measurement device, comprising: acondensing lens having a predetermined focal length; an image sensorconfigured to detect light passing through the condensing lens andoutput an image frame, the image sensor comprising: a pixel matrixcomprising a first pixel group and a second pixel group arranged in afirst direction and a second direction; a cover layer covering upon afirst region of a plurality of first pixels of the first pixel group andupon a second region of a plurality of second pixels of the second pixelgroup, wherein the first region and the second region are rectangles ofmirror symmetry along the first direction; and a plurality ofmicrolenses, each of the microlenses aligned with at least one of one ofthe first pixels and one of the second pixels; and a processorconfigured to divide the image frame into a first subframe, which isassociated with the first pixel group, and a second subframe, which isassociated with the second pixel group, calculate an offsetcorresponding to an image region in the image frame according to thefirst subframe and the second subframe, and calculate a depth of theimage region in the image frame according to the offset.
 2. The distancemeasurement device as claimed in claim 1, wherein the processor furthercomprises a storage unit configured to previously store a relationshipof a plurality of offsets and a plurality of depth differences from thepredetermined focal length.
 3. The distance measurement device asclaimed in claim 1, wherein the processor is further configured tocalibrate brightness of the first subframe and the second subframe to beidentical using a shading algorithm.
 4. The distance measurement deviceas claimed in claim 1, wherein the first region and the second regionare 5% to 95% of an area of a single pixel.
 5. The distance measurementdevice as claimed in claim 1, wherein the pixel matrix further comprisesa third pixel group and a fourth pixel group, the cover layer furthercovers upon a third region of a plurality of third pixels of the thirdpixel group and upon a fourth region of a plurality of fourth pixels ofthe fourth pixel group, and the third region and the fourth region arerectangles of mirror symmetry along the second direction.
 6. Thedistance measurement device as claimed in claim 5, wherein one of thefirst pixels, one of the second pixels, one of the third pixels and oneof the fourth pixels adjacent to each other form a sub pixel group, andthe first region, the second region, the third region and the fourthregion in the sub pixel group have identical areas.
 7. The distancemeasurement device as claimed in claim 6, wherein in two sub pixelgroups adjacent in the first direction and the second direction, thefirst region to the fourth region in a first sub pixel group are 50% ofan area of a single pixel, and the first region to the fourth region ina second sub pixel group are 5% to 45% or 55% to 95% of an area of asingle pixel.
 8. The distance measurement device as claimed in claim 5,wherein the first pixels are adjacent to the second pixels along adiagonal direction of the pixel matrix, and the third pixels areadjacent to the fourth pixels along another diagonal direction of thepixel matrix.
 9. A distance measurement method of a distance measurementdevice, the distance measurement device comprising a condensing lenshaving a predetermined focal length, a first pixel group, a second pixelgroup and a plurality of microlenses, the first pixel group and thesecond pixel group receiving incident light of different phases throughthe condensing lens and respectively through a first part and a secondpart of the microlenses, the distance measurement method comprising:outputting, by the first pixel group and the second pixel group, animage frame according to the predetermined focal length; dividing theimage frame into a first subframe and a second subframe, wherein thefirst subframe is associated with the first pixel group and the secondsubframe is associated with the second pixel group; calculating a firstoffset of a corresponded image region in the first subframe and thesecond subframe; and calculating a first depth of the image regionaccording to the first offset.
 10. The distance measurement method asclaimed in claim 9, wherein the first part and the second part are 5% to95% of each of the microlenses.
 11. The distance measurement method asclaimed in claim 9, wherein the distance measurement device furthercomprises a third pixel group and a fourth pixel group, the third pixelgroup and the fourth pixel group are configured to receive incidentlight of different phases through the condensing lens and respectivelythrough a third part and a fourth part of the microlenses, the firstpart and the second part are two opposite sides of the microlenses alonga first axis, and the third part and the fourth part are two oppositesides of the microlenses along a second axis.
 12. The distancemeasurement method as claimed in claim 11, further comprising: dividingthe image frame into a third subframe and a fourth subframe, wherein thethird subframe is associated with the third pixel group and the fourthsubframe is associated with the fourth pixel group; calculating a secondoffset of a corresponded image region in the third subframe and thefourth subframe; and calculating a second depth of the image regionaccording to the second offset.
 13. The distance measurement method asclaimed in claim 12, wherein one first pixel, one second pixel, onethird pixel and one fourth pixel adjacent to each other form a sub pixelgroup, in two sub pixel groups adjacent along the first axis and thesecond axis, the first part to the fourth part of a first sub pixelgroup are smaller than the first part to the fourth part of a second subpixel group, and the first depth and the second depth are obtainedaccording to the first sub pixel group, and the distance measurementmethod further comprises: calculating a third depth and a fourth depthaccording to the second sub pixel group; confirming the first depth withthe third depth; and confirming the second depth with the fourth depth.14. The distance measurement method as claimed in claim 12, wherein onefirst pixel, one second pixel, one third pixel and one fourth pixeladjacent to each other form a sub pixel group, in two sub pixel groupsadjacent along the first axis and the second axis, the first part to thefourth part of a first sub pixel group are different from the first partto the fourth part of a second sub pixel group, and the first depth andthe second depth are obtained according to the first sub pixel group,and the distance measurement method further comprises: calculating athird depth and a fourth depth according to the second sub pixel group,wherein the first depth and the second depth have a first resolution,and the third depth and the fourth depth have a second resolutiondifferent from the first resolution.
 15. The distance measurement methodas claimed in claim 11, wherein one first pixel, one second pixel, onethird pixel and one fourth pixel adjacent to each other form a sub pixelgroup, and in two sub pixel groups adjacent along the first axis and thesecond axis, the first part to the fourth part of a first sub pixelgroup are 50% of each of the microlenses, and the first part to thefourth part of a second sub pixel group are 5% to 45% or 55% to 95% ofeach of the microlenses.
 16. The distance measurement method as claimedin claim 11, wherein a plurality of first pixels of the first pixelgroup are adjacent to a plurality of second pixels of the second pixelgroup along a diagonal direction, and a plurality of third pixels of thethird pixel group are adjacent to a plurality of fourth pixels of thefourth pixel group along another diagonal direction.
 17. A distancemeasurement device, comprising: a condensing lens having a predeterminedfocal length; a pixel matrix comprising a first pixel group, a secondpixel group, a third pixel group and a fourth pixel group arranged alonga first direction and a second direction and configured to detect lightpassing through the condensing lens to output an image frame; a coverlayer covering upon the pixel matrix, the cover layer comprising: afirst cover pattern covering upon a first region of a plurality of firstpixels of the first pixel group; a second cover pattern covering upon asecond region of a plurality of second pixels of the second pixel group;a third cover pattern covering upon a third region of a plurality ofthird pixels of the third pixel group; and a fourth cover patterncovering upon a fourth region of a plurality of fourth pixels of thefourth pixel group; wherein the first region and the second region arerectangles of mirror symmetry along the first direction, and the thirdregion and the fourth region are rectangles of mirror symmetry along thesecond direction; and a processor configured to divide the image frameinto a first subframe, which is associated with the first pixel group,and a second subframe, which is associated with the second pixel group,calculate an offset corresponding to an image region in the image frameaccording to the first subframe and the second subframe, and calculate adepth of the image region according to the offset.
 18. The distancemeasurement device as claimed in claim 17, wherein one of the firstpixels, one of the second pixels, one of the third pixels and one of thefourth pixels adjacent to each other form a sub pixel group, and in twosub pixel groups adjacent along the first direction and the seconddirection, the first region to the fourth region of a first sub pixelgroup are 50% of an area of a single pixel, and the first region to thefourth region of a second sub pixel group are 5% to 95% of an area of asingle pixel.
 19. The distance measurement device as claimed in claim17, wherein the first pixels are adjacent to the second pixels along adiagonal direction of the pixel matrix, and the third pixels areadjacent to the fourth pixels along another diagonal direction of thepixel matrix.